The present invention relates generally to semiconductor packaging technology. The present invention has particular applicability to semiconductor packaging comprising a semiconductor chip attached to a substrate with an adhesive resin and electrically connected to bond fingers on the substrate.
Various types of semiconductor packages, such as a ball grid array (BGA) package, comprise a circuitized organic substrate having a solder mask thereon with exposed bond fingers. A semiconductor chip is attached to the substrate, typically via the solder mask, by an adhesive resin. Conventional solder masks comprise epoxy-based resins, acrylate-based resins and combinations of epoxy-based and acrylate-based resins. Typical adhesives for attaching the semiconductor chip to the substrate include epoxy-based adhesives, acrylate-based adhesives, silicones and polyimides. Although such adhesives are fairly viscous, they exhibit a tendency to bleed or spread over the surface of the underlying solder mask which exhibits a low surface tension and is designed to prevent bridging of solder material and shorting. The spreading or bleeding adhesive resin typically comes into contact with and covers a portion of the bond fingers exposed on the surface of the underlying substrate, thereby not only interfering with attachment of the bond wires to the bond fingers not causing short circuiting, since such die-attach adhesive resin is typically conductive and causes an undesirable reaction with the bond fingers.
A prior approach to this problem is disclosed by Fey et al. in U.S. Pat. No. 6,046,500 and comprises treating a surface of the substrate with a fluorine-containing plasma to reduce the spread of the adhesive resin onto preselected sites of the substrate surface.
There exists a continuing need for a simplified approach to the adhesive resin bleed problem that causes damage to and/or short circuiting of bond fingers on a circuitized substrate.
An advantage of the present invention is a circuit assembly comprising a solder mask structured to prevent a bleeding adhesive resin from coming into contact with bond fingers on the upper surface of a circuitized substrate.
Additional advantages and features of the present invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from the practice of the present invention. The advantages of the present invention may be realized and obtained as particularly pointed out in the appended claims.
According to the present invention the foregoing and other advantages are achieved in part by a circuit assembly comprising: a substrate having an upper surface; a plurality of bond fingers on the upper surface of the substrate; a solder mask on the upper surface of the substrate leaving the plurality of bond fingers exposed; a semiconductor chip attached to the upper surface of the substrate with an adhesive resin therebetween; and an opening in the solder mask extending between the semiconductor chip and the plurality of bond fingers, wherein the opening prevents the adhesive resin from coming into contact with any of the plurality of bond fingers.
Embodiments of the present invention comprise a solder mask having an opening in the form of a trough extending between at least one row of bond fingers and at least one side of the semiconductor chip and substantially parallel to the side of the semiconductor chip. Embodiments of the present invention further include a plurality of bond wires, each bond wire electrically connected between a bond pad on an upper surface of the semiconductor chip and a bond finger. Fabricated packages in accordance with embodiments of the present invention include a semiconductor chip attached to a solder mask on an upper surface of a circuitized organic substrate, with adhesive resin extending from under the semiconductor chip beyond the sides of the semiconductor chip and partially filling the trough such that the adhesive resin does not come into contact with any of the bond fingers.